As is known, data signals may be transmitted by amplitude modulating an optical signal in response to the data. The optical signal is typically generated by a semiconductor laser or light-emitting diode, propagates through a guiding medium, such as fiber, or through space, and is directly detected by a semiconductor photodiode. The optical signals commonly employed for data transmission have a wavelength which is located in the infrared portion of the electromagnetic spectrum. An example of an optical fiber data communication system is the Fiber Distributed Data Interface (FDDI) which transmits a continuous stream of data at 125 Mbit/sec. Examples of wireless optical data communication systems include: the ubiquitous TV/VCR remote control, which transmits bursts of pulses at a low effective bit rate and typically requires orientation of the transmitter; the BICC Communications InfraLAN, which transmits IEEE 802.5 token-ring standard data at a 4 Mbit/second rate and requires orientation of both the transmitter and receiver; and the Photonics Corporation Infrared Transceiver for Mobile Computing, which transmits data packets at a 1 Mbit/sec rate without requiring orientation. Wireless optical data communication systems, unlike their fiber counterparts, must contend with the presence of ambient light which, when detected, generates a direct current (dc) signal which may inhibit reception. In addition, the received signal power range of wireless optical data signals is significantly greater than the signal power range of optical data signals guided through fiber, especially if the propagation path of the wireless signals involves reflections which diminish the signal amplitude.
Since the release of the IEEE 802.3 10BASE-T twisted-pair Ethernet standard, 10 Mbit/sec Ethernet has rapidly become the de facto standard for local communication among PCs (personal computers) and workstations located on office desktops. Portable computers are now available which include provisions for the Ethernet controller function and 10BASE-T wired network connectivity. In addition, operating systems and software that incorporate file sharing permits portable computer users to convene and work together on a common document or other task if a limited-range wireless network could be readily established to link two or more computers together without requiring infrastructure. The use of a common format for both wired and wireless data minimizes the hardware and software complexity of both the portable computer and the wireless access ports connected to the wired network.
While Ethernet offers many advantages, eavesdropping is possible if the PC's Ethernet connection is a typical radio frequency (RF) transceiver. A typical RF transceiver has a transmission range of up to half a mile. Thus an eavesdropping receiver could be up to half a mile away and still intercept the PC's transmission. Such an interception would be almost impossible to detect. Due to the high transmission rate of Ethernet (10 Mbit/second), prior art wireless optical data communication systems are not readily usable for Ethernet because the transmission rate is much slower.
As a result, a need exists for a sensitive optical receiver for binary coded wireless optical data in a packet format, such as Ethernet, which minimizes ambient light degradation, has a wide acceptance angle so as to minimize the need to point or aim the receiver in a particular direction, and has a relatively short transmission range.